In Git, branches are simply pointers to a commit that move as new commits are added on that branch. In other words, once the pointer has moved, there is no memory that previous commits were on that branch. This was a hard concept for me to wrap my head around at first. Perhaps it's the name: "branch" makes me think of multiple nodes connected by edges, but in Git, a branch is really only a moving pointer to a node.
git log dutifully annotates commits with any branch that is pointing to them. For example, I created a repo with commits "one", "two", and "three" on branch master and "uno", "dos", and "tres" on branch feature, then merged feature back into master. Here's what git log tells me before I delete the branch:
* 9eb6e93 (HEAD, master) Merge branch 'feature'
|
| * 523e2ac (feature) tres
| * 6d3cc0f dos
| * 1bc0b2e uno
* | d39734b three
* | 779d37b two
* | facbcbf one
|/
* 58848f4 Initial commit.
It's easy to get fooled into thinking that the "(feature)" annotation is somehow referring to that branch on the right, but it's not: it's just referring to the commit 523e2ac.
Note that, by default, when Git creates a merge commit (9eb6e93 in our case), it automatically adds a comment stating that it's merging branch 'feature', so there is some record of there having been a branch there, but it's just a comment, nothing more.
When I delete the branch 'feature', nothing changes except that commit 523e2ac is no longer labeled with "(feature)":
* 9eb6e93 (HEAD, master) Merge branch 'feature'
|
| * 523e2ac tres
| * 6d3cc0f dos
| * 1bc0b2e uno
* | d39734b three
* | 779d37b two
* | facbcbf one
|/
* 58848f4 Initial commit.
So, to answer your question, no, once you've deleted a branch, you cannot get git log to annotate a commit with that branch name (because it doesn't exist anymore). However, you have some alternatives:
Don't delete the branch. There's no harm in leaving branches around, except that it clutters up your screen when you type git branch. Also, you may want to re-use branch names, which could cause problems later on if you don't delete your branches.
Tag the commit before you delete the branch. A tag is really a branch that doesn't move. You can even make the tag name the same as the branch name.
Satisfy yourself with the automatic commenting of merge commits. As mentioned before, when Git does a merge, by default, it references the name of the branch being merged in in the commit comment, creating a record that the branch existed. To me, this is the cleanest solution, based on the way branches work in Git. Since a branch doesn't really refer to a series of commits, it's really only of historical consequence that a branch existed.
The other place that branch history may linger is your reflog, which simply logs what branches you're switching to/from. It's mostly there for disaster recovery (ooops, I didn't mean to delete that branch!), and it's not really useful for the kind of branch history you're talking about.
